Trump did exactly that, when Jeb Bush was sitting high in all the polls back in 2016. Trump has moved the Republican base to the left since then, but with his support of gay marriage etc at a time that social issues are becoming urgent, he may be left behind, over towards the left, as the party moves back to the right.
Trump attacked from the RIGHT IN 2016. . Now he is attacking from the LEFT. It is his judgement that I question.
Trump led the polling right from the start, so he didn't run against the base. I bet you miss the Jeb Days? Sorry, the Bush stuff didn't work out for America. Time to move on.